Pajić, Z. et al.: The influence of inertial load application on kinematic and dynamic Sport Science 4 (2011) 1:

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1 THE INFLUENCE OF INERTIAL LOAD APPLICATION ON KINEMATIC AND DYNAMIC PERFORMANCES OF RUNNING AT MAXIMUM SPEED PHASE Zoran Pajić 1, Žarko Kostovski 2, Jelena Ilić 3, Saša Jakovljević 1 and Adem Preljević 4 1 University of Belgrade, Faculty of Sport and Physical Education, Serbia 2 University Ss Cyril and Metodius, Faculty of Physical Education, Skopje, Macedonia 3 Republic institute of sport, Serbia 4 State University of Novi Pazar, Serbia Original scientific paper Abstract The objective of this research was to produce changes in kinematic and dynamic performances of maximum running speed in training with additional inertial loads application, as well as to determine the adaptive processes that were supposed to significantly influence the maximum running speed in the observed variables. The change of kinematic variables recorded by non-contact telemetry measurement (twodimensional system) of a cycle of strides during sprint step in the phase of maximum running speed was analyzed, as a consequence of programmed training procedures application with an additional load at two different positions. The obtained results indicate that the applied experimental factor within the specific six week period caused statistically significant changes in experimental (EA) and (EL) groups. It is obvious that the different location of inertial load in experimental groups affected the changes in the observed variables differently, as well as that the applied additional load selectively affected the change in the observed variables. Key words : running speed, stride frequency, stride length Introduction It can be assumed that the kinematic and dynamic variables of maximum running speed change under the influence of additional loads, depending on their weight and fixing position. Different results were obtained about it, and they are probably caused by the application of different methodologies in researches. This implied the application of different load weight, the fixing position as well as various running speed at which experiments were conducted. However, in most researches the measurements were conducted at a moderate speed during treadmill running, with the exception of some in which the change of kinematic variables in terms of maximum speed and acceleration with the additional load was analyzed (Majdell & Alexander, 1991; Ropret et al., 1998). The results indicating increased frequency and reduced stride length were obtained in most papers (Rusko & Bosco, 1987; Cooke et al., 1991, etc.). The opposite results, when the frequency was reduced and stride length increased, have been reported in the researches (Stegman, 1981; Winter, 1983; Martin, 1985, etc.). The result when the increased arm load and leg load in particular caused a reduction in running speed, while the stride length remained unchanged and frequency reduced, was obtained (Ropret et al., 1998). In some studies the results showed no change in stride length and frequency (Catlin & Dressendorfen, 1979; Cavanagh & Kram, 1989; Martin & Cavanagh, 1990). Majdell & Alexander (1991) verified the change of the kinematics of 40 m running at a maximum speed, under the influence of training with the additional load. Six-week training with the additional load (10 pounds, 4.5 kg) was applied in the experiment. The treatment influenced the maximum speed of running to be statistically significantly increased (from 5.16 m/s -1 to 5:26), to shorten the contact phase (from 0.13 to 0.11sec), to statistically significantly reduce the upper leg angle of the take off leg in a moment of take-off (from 4.27 to 4.12 degrees), as well as and to increase the maximum angle of the lower leg flexion (from 2.62 to 3.28 degrees). The application of external load of participants during maximum speed running has already been suggested as a potential method of training (Bosco et al., 1986; Ropret et al., 1998; Pajić, 2000). Such a training of running at maximum speed with the additional load should be effective in order to enable the conversion of the increased muscle strength into muscle power (Delecluse et al., 1995; Ropret et al., 1998). The objective of this research was to analyze the effects of additional inertial load in the training process on the maximum running speed. The applied experimental factor should cause changes in kinematic and dynamic performances of maximum running speed in order to determine the adaptive processes in the observed variables. Methods Sample of participants The sample of participants in this study consisted of students of Faculty of Sport and Physical Education in Belgrade (Table 1). From the current population a sample of students was defined (n = 18). 107

2 With respect to the initial sprint time the participants were classified into three groups depending on the running speed. The groups were formed in attempt to make the equal abilities distribution among them. Table 1 Descriptive indicators for each group of participants AM for each group ± S.D. (N=6) Variables C EA EL Age 20.8± ± ±1.7 Height (cm) 176.3± ± ±8.12 Mass (kg) 69.36± ± ±8.5 50m - time (s) 6.83± ± ±0.44 C control group; (E-A) experimental group with arms load; E-L experimental group with legs load Measurement conditions and variables The system of three pairs of solar cells was applied for time parameters measurement measurement system (Brower timing system). The following variables were measured: Running speed in the maximum speed phase (VR), The average stride length in the maximum speed phase (SL), Stride frequency in the maximum speed phase (SF). For the number of strides (NS) measurement, the system of three video cameras was used, one of which recorded the distance of 25-50m in order to determine the number of strides between the first and the last contact, while the first and the last contact were identified by the other two cameras. The average stride length (SL) was calculated by dividing the distance between the first and the last foot contact with a number of strides. Stride frequency (SF) was calculated by dividing the speed of running with the length of strides. Based on the time for which the distance was run, the maximum speed of running was calculated (VR). For kinematic parameters measurement Mac Reflex 3.2 Measurement System Software with the Macintosh version 3.0 (for 2D and 3D system) was applied. The measurement procedure with this system provides a non-contact (telemetric) movement measurement. The basic principle of the system is recording the position of a number of well-defined points in space. Angle in Degrees A n g le v s T im e T im e in S e c o n d s 1-2 :2-3 Figure 1. Presentation of realised elbow joint angles in time (between the 1. and the 2. and 2. and 3. reflective markers on arm, while performing maximum running speed, obtained by telemetric measurements of the movement, using Mac Reflex system. The measured points are marked with reflective markers, and their movements are registered by a special video camera (Figure 1). The kinematic variables measured on the track in conditions of maximum running speed: angle in the knee joint center at take-off time (AKTT), angle in the knee joint center at the time of contact (AKTC), angle of maximum flexion of the lower leg during the back swing (AMFL), angle of maximum flexion of the forearm during the back swing (AMFA). Based on the previous measurements and software data acquisition with the applied software Mac Reflex 3D.V.3.1B2 and Microsoft Excel software adaptable, the values for variables (AKTT, AMFL, AMFA, and AKTC) were determined. The experiment protocol The experiment with parallel groups was carried out during which the effect of the experimental factor (inertial load) was on two levels. The first control group (C) realized the sprint training without additional load application. Second experimental group (EA) ran with the additional load attached to the arms. The third experimental group (EL) ran with the additional load attached to the legs. Experimental factor In order to increase the moment of the arms and legs inertia in the training procedure the additional load was applied in the form of bands with plates, fixed to the ankle and wrist. In line with previous researches and results (Catlin and Dressendorfen, 1979; Cavanagh & Kram, 1989; Stegemann, 1981; Martin, 1985; Ropret et al., 1998) a load of 1.8kg was applied, for which it was calculated that it changed the average torque inertia for about 50%. Testing procedure The research included initial and final measurements of all variables. Both measurements were realized in two days, the initial measurement (pre-test) one day prior to the beginning of training procedures application, and the final one two days after the end of the training procedure. The measurement of dynamic and kinematic variables was realized in running at maximum speed on the track from the 25 th to 50 th meter. Each participant ran two times, and for the final processing, better result was used. Measuring devices (photocells - Brower Timing System) were set at the start, to register the stand position start (0.5m), at 25m and at the end of 50m. The values were measured with an accuracy of 0.01 s. Training procedures After the warm up, the athletes performed their specific training procedures. During the six-weeklong experiment the trainings were performed three times a week. Training intensity was progressively increased, and the workload was increased after every two weeks. In the first two weeks, each participant was performing a series of five repetitions of their specific training regime. During the third and the fourth week of training the load was increased during two series, and in the last two weeks during three series of five repetitions. 108

3 Running was performed at maximum speed at 50m from semi-crouched position start with a 2-3 min. rest period between each run and with 8-10 min. of recovery between the series. Acquisition of experimental results Out of the descriptive statistical indicators, the measures of central tendency (arithmetic mean AM) as well as measures of dispersion (standard deviation - SD) were applied. Out of the qualitative methods of statistical analysis, the t-test for dependent samples was applied. The level of significance (p <0.05) was applied to determine the significance of differences between pre-test and post-test for each group. Statistical analysis was performed in the statistical program SPSS 16. Results and discussion Table 2. Descriptive statistics at the initial and the final measurement for the control group (C), experimental (EA) and experimental (EL) groups. vars. VR SL SF AKTT AKTC AMFL AMFA measur. control (C) experimental experimental M SD M SD M SD final initial final initial final initial final initial final initial final initial final initial Table 3: T- test for small dependent samples at the initial and the final measurement for the control group (C), experimental (EA) and experimental (EL) groups. control (C) experimental (EA) experimental. (EL) vars. t df t df t df VR SL SF AKTT AKTC AMFL AMFA The results of the descriptive statistics for all three groups at the initial and the final measurement are displayed in Table 2. The results of t-test for dependent samples at the initial and the final measurement are shown in the Table 3. It is evident that the applied training procedure in the phase of maximum speed did not cause statistically significant changes in the running speed (VR) in any group. From the above it is evident that the participants of the group (EL) reduced the running speed, but not within the range of statistical significance. The comparison of results from the initial and final measurements showed that there were no statistically significant changes in the observed variables in the control group. In the experimental groups there are statistically significant differences in variables for the average stride length (SL) as follows on average the participants had a lower score on the initial measurement (EA - p <.022) and (EL - p <.003) and the stride frequency variable (SF) the participants on average had higher scores on the initial measurement (EA - p <.002) and (EL - p <.000). Therefore, there was an extension of strides and the reduction of their frequency. If the running speed approaches the value of 7 m.s -1, the speed increases due to the increased stride length, provided that the frequency is not significantly changed (Jarić, 1997). The mentioned speed represents entering the zone of the upper limit for the maximum stride extension, because when running speed exceeds 7m.s -1, the stride length begins to grow more slowly, while at 8-9m.s -1 it reaches its maximum. The further speed increase is achieved by increasing stride frequency, which continues to grow rapidly, because only at the expense of its increase the maximum running speed is achieved (Luhtanen & Komi, 1978; Williams, 1985; Mero & Komi, 1985; Majdell & Alexander, 1991; Mero et al., 1992; Jarić, 1997). Apparently, the participants have reached the maximum speed of 8-9m.s -1, and thus the stride length. Given that there are no statistically significant changes in the speed of running (VR) in these groups, it can be assumed that the cause for that was statistically significant increased stride length, and consequently reduced number of strides, as well as reduced frequency of strides on the distance run, especially in groups (C) and (EL). The fall of frequency was probably due to the increased moment of inertia of legs, and thus to reduction of the angular speed of segments. The reasons for the speed reduction in the experimental group (EL) might be found in the assumption that the applied load caused an inadequate adaptation of the nervous system in movement control, i.e. there was a violation of techniques and movement coordination. Another reason could be a deficit of the speed (reactive) force which is necessary in the changed conditions of overcoming the gravitational forces, ground reaction forces and the inertia of the lower extremities. According to Stegman (1981), the increased moment of inertia results in lower natural frequency of the leg which acts like a pendulum. This suggests that the swing length increases, while the stride frequency is reduced. Under the assumption that the speed of motion is unchanged, the stride frequency reduction is followed by stride length increase. This claim was proved by Martin (1985) in an experiment - a load of 1 kg was applied on a foot, which increased the inertia moment by 13%.The inertial properties of a leg were significantly modified, the participants reluctantly adapted themselves to this new optimal stride frequency. Bobbert et al. (1986) stated that the insufficient leg speed in the swing, since it was burdened with inertia load, could be the limiting factor for further increase of the running speed. The assumption is that these changes are consequences of adaptation of the nervous system to manage movements with the 109

4 aim, in conditions of maintaining a constant speed, to create the most economical movement structure (frequency x stride length) for each type of load. The adaptation, among other things, due to inertia of the changed conditions for the legs, is performed in extended swing (resting) phase, which also causes the decrease of stride frequency. If the speed is the same or slightly decreased, any reduction of frequency results in the stride extension. It can be assumed that, together with the prolonged duration of training factor influence, there would be a correction in speed power expression, and consequently an easier correction of altered inertial conditions for the loaded leg. It would cause a better adaptation, i.e., more efficient movement realization in the changed conditions to overcome the gravitational forces, leg inertia and ground reaction forces, and thus the relative increase in movement frequency. This would probably increase the running speed. Based on the results presented, higher importance of frequency than stride length during running at maximum speed can be emphasized, which corresponds to the findings of many authors (Armstrong & Cooksey, 1983; Čoh, 1985; Mero, Komi, Rusko & Hirvonen, 1987; Mero & Komi, 1994; Ropret et al., 1998). The applied training procedures in the phase of maximum speed in the experimental groups (EA) and (EL) caused a statistically significant change of the knee joint center angle at the time of take-off variable (AKTT) in average, the participants in the initial measurement had lower scores (EA - p <. 000) and higher scores (EL - p <.042). For higher speed of running at the time of take-off it is very important that the critical angle of the body is greater at take-off, namely a greater knee joint angle at take-off (AKTT), i.e. lower flexion, because the effect of the horizontal component of ground force reaction on the speed of running in the ventral direction is more positive. From this follows that lowering the center of gravity causes greater flexion of the knee joint (AKTT), lower critical body angle and less positive effect of the horizontal ground reaction force in ventral direction. The results indicate that the angle increase in (EA) influenced positively, while the reduction in (EL) influenced the speed of running negatively. The applied training procedure of the experimental groups (EA) and (EL) caused a statistically significant change in the variable the center of the knee joint angle at the time of contact (AKTC) the participants on average had a lower score in (ER - p <.000) and higher score in the initial (EN - p <.000). During running, at landing and in the moment of contact with the ground (AKTC) a certain horizontal deceleration, i.e. speed reduction of the body center happens, namely a depreciation phase is realized. For greater speed of running at the moment of contact with the ground it is essential that the body angle upon contact is less critical, namely a greater knee joint angle at contact (AKTC) i.e. lower flexion, because it reduces the negative impact of the horizontal component of ground force reaction on the speed of running in the dorsal direction. The results indicate that the increase in angle in (EA) influenced positively, while the reduction in (EL) influenced the speed of running negatively. From the aforementioned results it is noted that the participants in the experimental group (EL) increased the average angle of maximum flexion of the lower leg during the last swing (AMFL) within the statistical significance the participants on average had a lower score on the initial (EL - p <.000). This change has a negative effect on running speed since the moment of leg inertia is increased, the angular speed and thus the leg frequency are reduced. The maximum forearm angle flexion during the back swing (AMFA) changed significantly the participants on average had higher scores in the initial measurement (EA - p <.000) and lower scores (EL - p <.011). Since smaller angle reduces the moment of arm inertia, greater speed is achieved, that is, a shorter duration of arm swing phase. This results in body segments movement frequency increase, i.e., in positive impact on higher running speed. It is interesting that, despite the foregoing, the experimental group (EL) significantly increased the average angle of maximum forearm flexion during the back swing (AMFA) within the statistical significance. It could be expected that the participants would adapt themselves to the changed inertia conditions and make adequate flexion of the elbow joint, reduce the angle and moment of inertia. However, due to the significant increase of leg flexion angle in the swing phase, and thus the moment of inertia, probably due to synchronous activity of collateral limbs, the increase of position moment of arms inertia represents a compensating attempt to counter the increased inertia forces of the leg moving in the opposite direction. Therefore, this could affect better movement synchronization of contra lateral segments, to a more stable overall movement of a lever system of the entire body. The increased arms frequency that counters legs frequency causes higher level of neural activity (reciprocal inhibition) and thus affects the kinematics of the legs. Table 4: Descriptive statistics for all three groups of participants at the final measurement control (K) experimental (EA) experimental (EL) vars. M SD M SD M SD VR SL SF AKTT AKTC AMFL AMFA Bearing in mind that the reduction of the swing amplitude is more possible in the elbow joint than in the knee and hip joints (Majdell & Alexander, 1991), it can be assumed that these adaptive processes, as a result of arm load, can influence the change in leg kinematics. The results of the descriptive statistics for all three groups at the final measurement are shown in the Table

5 Table 5. T- test for small independent samples among all three groups at the final measurement t C-EA C-EL EA-EL df t df t df tailed tailed vars. VR SL SF AKTT AKTC AMFL AMFA The comparison of the final measurement results for all three groups in all variables are shown in Table 5. There are statistically significant differences between the control group (C) and experimental group (EA) and the experimental group (EL) in the following variables: the center of the knee joint angle at the time of take-off (AKTT) the participants in the control group (C) on average had a lower score than the participants in the group (EA) - (p <.022), while the group of participants (EL) on average had a lower score than the participants of the group (EA) - (p <.000); the center of the knee joint angle at the time of contact (AKTC) the participants in the control group (C) on average had a lower score than the participants in the group (EA) (p <.007), while the group of participants (EL) on average had a lower score compared to the athletes in the group (EA) (p <.000). The angle of maximum lower leg flexion during the back swing (AMFL) the participants in the control group (C) on average had a lower score than the participants of the group (EL) (p <.005); The angle of maximum forearm flexion during the back swing (AMFA) the participants in the control group (C) on average had higher scores than the participants of the group (EA) (p <.006) and lower score in comparison to the participants of the group (EL) (p <.004). The participants in group (EL) on average had higher scores than the participants of the group (EA) (p <.000). It is evident that the key differences between the groups were in the last variable (AMFA) and that the effect of the experiment was the most prominent there. Additionally, for (EA) group the significant results are the variables of the center of the knee joint angle at the time of take-off (AKTT) and the center of the knee joint angle at the time of contact (AKTC), since they are significantly different for this group unlike for the other two groups. For (EL) group the characteristic variable is the angle of maximum lower leg flexion during the back swing (AMFL), but only in relation to the control (C). Conclusion The change of kinematic variables recorded by noncontact telemetric measurement (two-dimensional system) of one cycle of strides during sprint strides in the phase of maximum running speed was analyzed, as a consequence of programmed training procedures application with an additional load at two different places. The obtained results indicate that the applied experimental factor in the specific six week period caused statistically significant changes in experimental (EA) and (EL) groups. It is obvious that the different place of inertial load in the experimental group affected differently the changes in the observed variables, as well as that the applied additional load selectively affected the change of the observed variables. The applied load significantly influenced the kinematic variables, the influence of which is obvious for factors that favor, as well as those that interfere with the performance of maximum running speed efficiency (angular momentum, moment of inertia, force reaction, gravity, the effects of one-joint and biarticulated muscles, body movement activities, kinetic chain activities). We can assume that the variables AKTT, AKTC, AMFL and AMFA are predictable for the maximum running speed and that there is their significant connection with running at maximum speed. The results of this study face a new dilemma. It is not clear whether the same load for arms and legs is adequate, since the arm adjustment to the changed conditions of moment of inertia, and therefore the gravitational forces is much higher compared to the leg adjustment, as well as whether different time is needed for full adaptation of both arms and legs. In this research an attempt to increase the momentum by changing the inertia conditions is significant. Momentum cannot be improved by higher moment of inertia that is created when applying even a very small additional load (even if it is only a few hundred grams), especially if applied at the end of the kinetic chain, because in this case very inadequate high angular velocities are obtained. The introduction of the absolute value of the load, without calculating the actual mass of each locomotive apparatus individually, raises doubts because the moment of inertia increases by mr 2, i.e., the value of the applied load is squared, even if it is only one gram. 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